Li-ion pouch cells provide very high energy density but can suffer from degradation due to excessive or non-uniform heating of the electrode stack, particularly for thicker cells. For example, very thick cells when discharged at high rate will reach a much higher temperature in the center of the cell relative to the outer layers of the cell. Also in a rapid thermal event, it is often very difficult to remove the heat quickly enough to prevent thermal runaway and related safety issues. Typically cells are cooled by using thermally conductive plates, such as Aluminum plates, placed in contact against one or both of the flat faces of the Li-ion pouch cell. It is also known that cells can be partially cooled or heated using the tabs that exit the pouch cell and carry the electrical current during charge and discharge since thermal conduction parallel to the face of the cell along the metal current collectors to the tabs is much greater than thermal conduction from the center of the cell to the face through the many electrode and separator layer interfaces. However, it is desirable to separate thermal and electrical pathways to enable independent optimization of the system design relative to these parameters. Also cells with lower impedance are less likely to heat up.
However, these solutions to addressing thermal management and control in Li-ion battery applications can lead to a major decrease in the cell energy density because of the extra volume and weight of the tabs or cooling plates or the increase in the number of thinner, lower capacity or lower impedance cells required to meet the energy demands of an application. These solutions can also lead to additional cost of the overall battery system. It is also well known that it is difficult and expensive to increase the size or number of tabs or other thermally conductive elements passing through the Aluminum laminate packaging seal due to manufacturing complications and the increasing likelihood of leaks forming around the area where the tab passes through the seal. The cells become more susceptible to failure as the number and size of elements, such as tabs, passing through the pouch cell seal is increased. A solution for increasing thermal access to the inside of pouch cells for cooling or heating while minimizing the impact on cell energy density, performance or life is needed.